1. Field of the Invention 
The present invention relates to a circular cutter, more particularly to a circular cutter with a tiltable cutter-holding arm which is pivoted to a bracket-holding part of a base plate through a friction-providing plate. 
2. Description of the Related Art 
Referring to FIG. 1, a conventional circular cutter is shown to include a base plate 10, a bracket-mounting element 12, a pivot shaft 132, a bracket 13, a cutter-holding arm 14, and a cutter-tilting lock. 
The base plate 10 is made from aluminum, and is formed with a recess 111 and a pair of screw holes 112. The bracket-mounting element 12 is made from cast iron, is disposed in the recess 111, and is fixed to the base plate 10 through threaded engagement between two locking bolts 121 and the screw holes 112 in the base plate 10. The bracket-mounting element 12 is formed with an inner thread, and defines a first abutting face that is transverse to the base plate 10. The bracket 13 is pivoted to the bracket-mounting element 12 through the pivot shaft 132, which extends in a transverse direction relative to the first abutting face of the bracket-mounting element 12. The bracket  13 defines a second abutting face that confronts the first abutting face of the bracket-mounting element 12, and is formed with an arcuate slot. The cutter-holding arm 14 is pivoted to two lugs 131 of the bracket 13. A locking bolt 15 of the cutter-tilting lock extends through the arcuate slot in the bracket 13 and engages threadedly the inner thread of the bracket-mounting element 12 in such a manner that tightening of the locking bolt 15 results in tight abutment between the first abutting face of the bracket-mounting element 12 and the second abutting face of the bracket 13, thereby preventing rotation of the bracket 13 about the pivot shaft 132, and that loosening of the locking bolt 15 results in disengagement between the first and second abutting faces, thereby permitting adjustment of the cutter-holding arm 14 to a desired position relative to the base plate 10. 
One disadvantage of the conventional circular cutter resides in that since the base plate 10 is made from aluminum, which is relatively soft, it is not strong enough to hold the bracket-mounting element 12 thereon. Besides, constant vibration of the bracket 13 relative to the bracket-mounting element 12 during cutting operations may result in loosening of the locking bolts 121 and wear of the threads in the screw holes 112.  